Shorting switch mechanism



Sept. 21, 1965 T. ELLIOTT 3,208,021

' SHORTING SWITCH MECHANISM Filed Sept. 12, 1962 2 Sheets-Sheet 1 Sept.21, 1965 T. ELLlOTT SHORTING SWITCH MECHANISM 2 Sheets-Sheet 2 FiledSept. 12, 1962 Pies United States Patent 3,208,021 SHORTING SWITCHMECHA-NiSM Theodore Elliott, Brooklinc, Mass, assignor to AstraCorporation, Boston, Mass, a corporation of Massachusetts Filed Sept.12, 1962, Ser. No. 223,077 2 Claims. (Cl. 336-107) This inventionrel-ates to instrument transformers and more particularly to shortingswitch mechanisms part-icularly useful with current transformers.

Current transformers are utilized to measure or monifor relatively heavyelectrical currents flowing in a conductor. Typically the conductor ismade a primary winding and a secondary Winding having a multiplicity ofturns is inductively coupled to the primary winding. The voltage inducedin the secondary winding is an accurate measure of the current flow inthe primary. When the secondary winding of such a current transformer isopen and energized there is a high potential between its terminals evenwhere no current is flowing in the secondary winding. In order to workon such devices safety precaution-s demand that the secondary winding beclosed (shorted). A variety of devices are employed in the art such asthrow over links or clips, which often are awkward to use, frequentlyrequire insulated tools of some kind to manipulate the shorting element,and in some cases the shorting element is a loose part which may bemisplaced or lost.

Accordingly, it is an object of this invention to provide a new andimproved current transformer shorting mechanism.

Another object of the invention is to provide a novel and improvedcurrent transformer shorting switch mechanism which is safe and easy tooperate and does not require tools.

A further object of the invention is to provide an improved instrumenttransformer terminal shorting mechanism which may be operated withoutexposing the terminals.

Still another object of the invention is to provide a compact instrumenttransformer shorting mechanism which may be easily secured in positionand sealed to deter tampering.

A further object of the invention is to provide a new and improvedinstrument transformer shorting mechanism which provides positiveindication of the position of the shorting mechanism and is arranged tominimize the possibility that the mechanism be inadvertently left inshorted condition.

In accordance with the invention there is provided in combination with acurrent transformer having secondary terminals brought out to a surfacethereof, an electrically insulating actuator cap arranged to enclose theterminals and to operate the shorting switch mechanism. The

shorting switch mechanism is secured to the transformer case and ismovable by the cap between a shorting position and an open circuitposition. The cap is also arranged for positioning in a seated or lockedposition and a released position in which the switch can be operated bymanipulation of the cap. This structure is a safe and easy to operatestructure which does not require any tools for a technician to operate.It completely encloses the transformer terminals so that they are notaccessible through accident or inadvertence. Further, the mechanism istamper proof as the cap may be sealed in position by conventional meanseither with the terminals connected to external metering circuitry forexample or locked in short circuited position with the indication of theswitch position clearly evident. Thus there is provided a novel andimproved instrument transformer shorting mechanism.

In the preferred embodiment of the invention the instrument transformersecondary winding is in the form of a toroid which has two secondaryterminals brought out through a rectangular top surface of thetransformer casing. A rotatable shorting switch mechanismis positionedbetween the two terminals and has two opposed legs which cooperate inwiping engagement with flat conductive surfaces of the terminals. Theswitch mechanism is rotatable between a shorting position and an opencircuit position. Detent means are provided in the top surface of thecasing to aid in positioning the shorting switch member in the shortingposition or in the open circuit position. A resilient couplingcooperates with the switch mechanism and engages a boss on an actuatorcap that is formed in rectangular configuration similar to theconfiguration of the top surface of the transformer. This boss may bemoved axially relative to the shorting switch mechanism between a firstposition which the cap is directly seated on the top surface and araised position. Also provided on the top surface are a series of tabswhich cooperate with the skirt wall of the cap to prevent its rotationwhen it is seated, thus positively positioning the cap and shortingswitch mechanism. When the cap is moved to the raised position the bossis still in engagement with the shorting switch mechanism but is clearof the tabs on the transformer surface so that it is free to be rotated.The cap skirt wall has two out out portions through which wiresconnected to the terminals can pass. The cap and boss are arranged sothat these out out portions are aligned with the tabs when the shortingswitch mechanism is in the shorting position so that the cap cannot beseated on the top surface properly if there are external connections tothe terminals. This provides a positive indication of the position ofthe shorting switch cap controlmember. In addition, there is providedsecuring means in the cap which acts to pull the cap down into seatingrelation with the top surface of the transformer in which position asea-ling wire may be employed to seal the cap and switch mechanism inthe desired position (positively enclosed either in circuit or out ofcircuit) so that unauthorized accessibility to the terminals and to theshorting switch mechanism is prevented. Thus the invention provides asimple, safe, attractive and easy to operate shorting switch mechanism.

Other objects, features and advantages of the invention will be seen asthe following description of a preferred embodiment of the inventionprogresses, in conjunction with the drawings, in which:

FIG. 1 is a perspective view of a current transformer and shortingswitch mechanism constructed in accordance with principles of theinvention;

FIG. 2 is a top view of the current transformer shorting switchmechanism in open circuit position with the operating cap removed;

FIG. 3 is a sectional view along the line 3--3 of FIG. 1 with the cap inplace in seated relation on the top surface of the current transformerhousing;

FIG. 4 is an exploded view of components of the rotatable shortingswitch structure;

FIG. 5 is a perspective view of the cap in inverted position with aportion thereof broken away; and

FIG. 6 is a sectional view of a portion of the cap.

With reference to FIG. 1 there is shown a current transformer having acasing 10* of conventional electrical insulation material such as moldedepoxy resin mounted on a base 12 for securing to a suitable support.Within the case 10 is a secondary winding wound in toroidal shape sothat an aperture 14 is provided in the case through which a primaryconductor may pass. Terminals of the secondary winding are connected tostuds 16, 18 which are brought out of the top surface 20 of the currenttransformer casing. The configuration of the top surface is square inthe preferred embodiment as best indicated in FIG. 2. Molded in the topsurface 20 on either side of each terminal stud and in slightly from theedge of the surface are two aligned tabs 22. Also molded into the topsurface at each corner are receptacles 24 to receive studs for mountinga conduit box adjacent the terminals if desired.

7 Each terminal 16, 18 is in the form of a stud and has a flatwasher-like member 26 seated on the transformer top surface whichincludes a flat surface 28 that extends inwardly towards the otherterminal stud. This member is secured on the stud by means of a firstnut 30. Immediately above this nut are two washers 32, 34 which aresecured in place by a second nut 36. Conventionally a conductor isattached to each terminal stud between the washers and then the uppernut 36 is tightened down on the washers to secure the electricalconductor in positive electrical relation to the terminal.

Positioned centrally between the terminals 16, 18 is a shorting switchmechanism which includes a stud 40 secured to the casing in suitablemeans as by molding the lower portion 42 (FIG. 4) directly into theepoxy material. An intermediate portion 44 of the stud is formed as aseating and bearing element and the upper portion 46 is threaded.Mounted on the intermediate portion 44 is an electrically insulatingwasher 48 which has a lower flange 50 and an upstanding collar portion52. Positioned immediately above and seated on the flange 50 of thewasher 48 with the hollow portion protruding through a central aperture54 is a oouplingmember 56 which has two upstanding side walls 58, 60.Each side wall has a detent portion 62 in the form of a V. A bridgingmember 64 of suitable conductive material, phosphor bronze for example,has a central aperture 66 which also is spaced from stud 40 by thecollar portion 52 of the insulating washer 48 when its intermediateportion with straight side walls 68 is fitted inside the side walls 56,58 so that positive alignment is maintained between the coupling member56 and the bridging member 64. The bridging member has opposed legs 70,72 which extend outwardly and slightly downwardly from the plane of theintermediate portion to provide resilient'wiping surfaces 74 which maybe disposed in engagement with the terminal elements 28 in a shortingposition. The edges of the wiping surface portions are in the form ofturned up flanges 76 which enable the legs to easily ride up over thearcuate guide ridges 80 that are molded in the top of the transformercasing. A second electrically insulating washer 86 fits over the collarportion 52 of the washer 48 and a nut 88 engages the threaded portion 46of the stud to secure the several components of the switching mechanismtogether on the stud 40.

Positioned over the terminals and the shorting switch structure is aswitch actuator in the form of a cap 90 of suitable material, which inthis embodiment is of a square configuration corresponding to theconfiguration of the top surface 20 of the transformer casing. This caphas a depending skirt 92 which extends around the entire periphery ofthe cap and has a lower edge surface 94 that is seated on surface 20outside of tabs 22. Also in one wall of the skirt near the seatingsurface are two out :out aperture portions 96 which in one position ofthe cap are aligned with the two of the tabs 22. Centrally locatedwithin the cap is a boss 98 which has two parallel side walls 100 whichare adapted to receive the side walls 58 of the coupling member 56. Eachwall 100 has a groove 102 that receives a detent 62 when the cap is in araised position. A central aperture 104 is provided within the boss andsecured in this aperture 104 is a securing member 106 which has aknurled knob 108 and a hollow shank 110, the lower portion of whichforms a guide for stud 40 and the intermediate portion of which hasthreads to engage the threaded portion 46 of stud 40. This securingmember 106 is secured in the cap by means of a resilient locking disc114. A washer 116 is provided underneath the knurled knob. Immediatelybelow the knob 108 there is a section which has a plurality of radiallyextending through passageways 118 which may be aligned with apertures120 in the cylindrical wall 122 on which the washer 116 seats. A sealingwire may be passed through the apertures 120' and one of the passageways118 to positively lock the securing member 106 relative to the cap 90.

When the cap is in seated position the tabs 22 are immediately insidethe skirt wall 92 so that rotation of the cap is prevented. In order tooperate the shorting switch mechanism the threaded securing 106 must befreed to permit the cap to be raised on the switch coupling member sidewalls 58, 60 until detent portion 62 engages the grooves 102 in theboss. In this position the lower edge 94 of the skirt clears the uppersurface of the tabs and the cap may be rotated. The arcuate ridgesmolded into the upper surface of the transformer housing provide a guideto aid in insuring rotation of the switch mechanism. In addition, theskirt wall is again lined up with the periphery of the top surface ofthe transformer when 90 rotation has been accomplished, thus providing apositive indication of switch position.

In FIGS. 1-3 the transformer shorting switch is shown in the opencircuit position with the leg portions 70, 72 out of contact with theterminal surfaces 28.. With rotation of the bridge member through 90 thetwo opposed legs 70, 72 contact the surfaces 28 and provide a directshort thereacross to remove any potential difference that may existbetween the two terminals. The cap then can be removed by snapping thespring detents 62 out of the grooves 102 in a simple manner and thewiring on the terminals adjusted orchecked as desired. After inspectionand/or adjustment, the cap can be placed back on the shorting switchmechanism only in the same position, due to the cooperatingconfiguration of the coupling member 56 and boss 98. The cap then isscrewed down by means of the threaded securing 106. However, if theswitch element is left in the shorted position the apertures 96 in theskirt are aligned with the tabs 22 (as the cap is rotated 90 from theposition shown in FIG. 1) and if there are any wires connected to theterminals the cap cannot be seated on the transformer top surface. Thisprovides positive indication of the position of the shorting switch.Further, if the transformer is out of service and no connections are tobe made the cap may be left in the shorted switch position so that thetabs are aligned with the cut outs and the terminals are totallyenclosed and are not accessible to tampering or other unauthorizedaccess.

Thus it will be seen that the invention provides a compact shortingswitch mechanism, reliable and simple in operation which providespositive control over accessibility to the terminals of the instrumenttransformer. While a preferred embodiment of the invention has beenshown and described, various modifications thereof will be obvious tothose skilled in the art and therefore it is not intended that theinvention be limited to the disclosed embodiment or to details thereofand departures may be made therefrom within the spirit and scope of theinvention as defined in the claims.

I claim:

1. An instrument current transformer having a secondary winding in theform of a toroid to provide an axial opening adapted to receive aconductor which extends through the opening and functions as a primaryconductor,

an outer casing of molded electrical insulation sur rounding saidsecondary winding,

a support base secured to said .outer casing,

the top of said casing being substantially flat and having two secondarywinding terminals extending upwardly therefrom,

each terminal including means for fastening a conductor thereto and aconductive wiping surface disposed substantially in the plane of saidtop surface,

a shorting switch structure positioned between said secondary terminals,

said shorting switch structure including an upstanding stud secured insaid outer casing,

an electrically conductive bridging element having opposed legs mountedfor rotation on said stud,

said bridging element being rotatable between a first position wheresaid legs are in Wiping engagement with said teminal wiping surfaces anda second position where said legs do not short said terminals,

means comprising spaced ridge portions disposed along the circular pathof movement of said bridging element legs, the spaces between said ridgeportions receiving said bridging element legs for positive posit-ioningin said first and second positions,

two aligned upstanding tabs positioned on said casing top surfaceoutside of each terminal,

means to insulate said bridging element from said upstanding studcomprising a flanged electrically insulating washer and a secondelectrically insulating washer,

a resilient coupling element having two upstanding spaced parallel sidewalls secured to said bridging element for rotation therewith,

thread means in the upper end of said stud,

a rotatable cap having a centrally located boss adapted to be disposedbetween said coupling element side Walls for cooperative engagementtherewith,

threaded securing means positioned in said boss for engagement with saidstud thread means to secure said cap to said stud,

said cap having a depending skirt wall extending entirely therearoundadapted to seat on said top surf-ace outside of said terminals,

said skirt wall having two spaced cut out portions in the seatingsurface of one portion of said skirt wall,

said cut out portions providing paths for electrical conductorsconnected to said terminals to extend externally of said cap when saidcap is seated on said casing top surface and said bridging element is insaid second position, and

said cut out portions being aligned with said tabs when said bridgingelement is in said first position so that conductors connected to saidterminals prevent said cap from being seated on said casing top surface,

said tabs preventing rotation of said cap and said shorting switchstructure when said cap skirt wall is seated on said top surface,

and said threaded cap securing structure permitting said cap to beraised without disengaging the cap from the shorting switch structure sothat said cap may be rotated to move said shorting switch structurebetween said first and second positions,

and means cooperating with said threaded securing structure to receivesealing wire for locking said cap on said casing top surface to preventunauthorized accessibility to said terminals and tampering with saidshorting switch structure.

2. An instrument current transformer having a secondary Winding in theform of a toroid to provide an axial opening adapted to receive aconductor which extends through the opening and functions as a primaryconductor,

an outer casing of molded electrical insulation surrounding saidsecondary winding,

a support base secured to said outer casing,

a surface of said casing being substantially fiat and having twosecondary winding terminals extending upwardly therefrom,

each terminal including means for fastening a conductor thereto and aconductive switch surface,

a shorting switch structure positioned between said secondary terminals,

said shorting switch structure including means defining a switch pivotaxis secured in said outer casing,

an electrically conductive bridging member mounted for rotation on saidpivot axis defining means,

said bridging member being rotatable between a first position in whichsaid bridging member electrically contacts said terminal switchsurf-aces to provide a short circuit position therebetween and a secondposition to provide an open circuit between said terminal switchsurfaces,

means for positively positioning said bridging member in said first andsaid second positions,

a resilient coupling element secured to said bridging member forrotation therewith,

a rotatable cap having a means for receiving said coupling element and adepending skirt wall extending entirely therearound adapted to seat onsaid surface of said casing outside of said terminals,

said skirt wall having two spaced out out portions for providing pathsfor electrical conductor-s connected to said terminals to extendexternally of said cap when said cap is seated on said casing surfaceand said bridging member is in said second position,

two upstanding tabs fixed in position on said casing surface and alignedwith said out out port-ions of said cap when said bridging member is insaid first position to prevent said cap from being seated on said casingtop surface when conductors are connected to said terminals,

said tabs preventing rotation of said cap and said shorting switchstructure when said cap skirt wall is seated on said casing surface,

a cap securing structure having a first position for securing said capin seated position on said casing surface,

a second position permitting said cap to be raised to allow said skirtwall to clear said tabs without disengaging the cap from said couplingelement so that said cap may be rotated to move said shorting switchstructure between said first and second positions,

and means cooperating with said securing structure for locking said capsecuring structure in said first position to prevent unauthorized accessto said terminals and tampering with said shorting switch structure.

References Cited by the Examiner UNITED STATES PATENTS 1,667,617 4/28Zelt 200-168 X 1,786,746 12/30 Gibbs 200-168 X 2,589,084 3/52 Hoffman200--155 2,672,532 3/54 Robinson 20051.08 X 3,098,133 7/63 J. Van DenDriest ZOO-51.07

JOHN F. BURNS, Primary Examiner,

2. AN INSTRUMENT CURRENT TRANSFORMER HAVING A SECONDARY WINDING IN THEFORM OF A TOROID TO PROVIDE AN AXIAL OPENING ADAPTED TO RECEIVE ACONDUCTOR WHICH EXTENDS THROUGH THE OPENING AND FUNCTIONS AS A PRIMARYCONDUCTOR, AN OUTER CASING OF MOLDED ELECTRICAL INSULATION SURROUNDINGSAID SECONDARY WINDING, A SUPPORT BASE SECURED TO SAID OUTER CASING, ASURFACE OF SAID CASING BEING SUBSTANTIALLY FLAT AND HAVING TWO SECONDARYWINDING TERMINALS EXTENDING UPWARDLY THEREFROM, EACH TERMINAL INCLUDINGMEANS FOR FASTENING A CONDUCTOR THERETO AND A CONDUCTIVE SWITCH SURFACE,A SHORTING SWITCH STRUCTURE POSITIONED BETWEEN SAID SECONDARY TERMINALS,SAID SHORTING SWITCH STRUCTURE INCLUDING MEANS DEFINING A SWITCH PIVOTAXIS SECURED IN SAID OUTER CASING, AN ELECTRICALLY CONDUCTIVE BRIDGINGMEMBER MOUNTED FOR ROTATION ON SAID PIVOT AXIS DEFINING MEANS, SAIDBRIDGING MEMBER BEING ROTATABLE BETWEEN A FIRST POSITION IN WHICH SAIDBRIDGING MEMBER ELECTRICALLY CONTACTS SAID TERMINAL SWITCH SURFACES TOPROVIDE A SHORT CIRCUIT POSITION THEREBETWEEN AND A SECOND POSITION TOPROVIDE AN OPEN CIRCUIT BETWEEN SAID TERMINAL SWITCH SURFACES, MEANS FORPOSITIVELY POSITIONING SAID BRIDGING MEMBER IN SAID IRST AND SAID SECONDPOSITIONS, A RESILIENT COUPLING ELEMENT SECURED TO SAID BRIDGING MEMBERFOR ROTATION THEREWITH, A ROTATABLE CAP HAVING A MEANS FOR RECEIVINGSAID COUPLINGELEMENT AND A DEPENDING SKIRT WALL EXTENDING ENTIRELYTHEREAROUND ADAPTED TO SEAT ON SAID SURFACE OF SAID CASING OUTSIDE OFSAID TERMINALS, SAID SKIRT WALL HAVING TWO SPACED CUT OUT PORTIONS FORPROVIDING PATHS FOR ELECTRICAL CONDUCTORS CONNECTED TO SAID TERMINALS TOEXTEND EXTERNALLY OF SAID CAP WHEN SAID CAP IS SEATED ON SAID CASINGSURFACE AND SAID BRIDGING MEMBER IS IN SAID SECOND POSITION, TWOUPSTANDING TABS FIXED IN POSITION ON SAID CASING SURFACE AND ALIGNEDWITH SAID CUT OUT PORTIONS OF SAID CAP WHEN SAID BRIDGING MEMBER IS INSAID FIRST POSITION TO PREVENT SAID CAP FROM BEING SEATED ON SAID CASINGTOP SURFACE WHEN CONDUCTORS ARE CONNECTED TO SAID TERMINALS, SAID TABSPREVENTING ROTATION OF SAID CAP AND SAID SHORTING SWITCH STRUCTURE WHENSAID CAP SKIRT WALL IS SEATED ON SAID CASING SURFACE, A CAP SECURINGSTRUCTURE HAVING A FIRST POSITION FOR SECURING SAID CAP IN SEATEDPOSITION ON SAID CASING SURFACE, A SECOND POSITION PERMITTING SAID CAPTO BE RAISED TO ALLOW SAID SKIRT WALL TO CLEAR SAID TABS WITHOUTDISENGAGING THE CAP FROM SAID COUPLING ELEMENT SO THAT SAID CAP MAY BEROTATED TO MOVE SAID SHORTING SWITCH STRUCTURE BETWEEN SAID FIRST ANDSECOND POSITIONS, AND MEANS COOPERATING WITH SAID SECURING STRUCTURE FORLOCKING SAID CAP SECURING STRUCTURE IN SAID FIRST POSITION TO PREVENTUNAUTHORIZED ACCESS TO SAID TERMINALS AND TAMPERIN WITH SAID SHORTINGSWITCH STRUCTURE.